A floor structure for a vehicle body in which a fuel tank is disposed below a front seat of a vehicle via a floor panel is disclosed in JP-A-2002-302071. The floor panel has a raised part that protrudes upward and is formed in a region that corresponds to a region below the front seat. The raised part increases the bending rigidity of the floor panel in a width direction of the vehicle. An accommodating concavity is formed on a rear surface side of the floor panel by the raised part. A fuel tank is accommodated in the storage concavity.
In the floor structure described above, the fuel tank is preferably enclosed by cross members and left and right floor frames for supporting the floor panel. The left and right floor frames extend in a longitudinal direction of the vehicle body, and the cross members extend between the left and right floor frames in an orthogonal fashion. For this reason, when a load is applied to the floor frame from the front of the vehicle body, the load is transmitted from the floor frame to the cross members, in which case the load is transmitted while the transmission direction undergoes a marked change.
Thus, it is difficult to transmit an impact to the cross members in a smooth fashion in the above-described floor structure. Therefore, a relatively large load is placed on the floor frame. The relatively large load placed on the floor frame must be supported by the floor frame, and the rigidity of the floor frame must be increased.
Therefore, designing the floor structure so as to increase the rigidity of the floor frame will be a factor in hampering efforts to reduce the weight of the floor structure for a vehicle body.